Heat transfer system

ABSTRACT

A heat storage and/or recovery system using multiple heat storage tanks to selectively store heat from a solar collector and recover the stored heat to operate a heat driven system. The heat from the solar collector is transferred into the storage tanks through an input heat transfer link configuration using vapor heat transfer which automatically transfers heat into a storage tank that will accept the heat but effectively prevents the flow of heat from the storage tanks back to the solar collector while the heat in the storage tanks is transferred to the heat driven system through a recovery heat transfer link configuration also using vapor heat transfer which automatically transfers heat to the heat driven system from a storage tank capable of supplying heat but effectively prevents the flow of heat from the heat driven system back into the storage tanks.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of my co-pending application Ser. No.615,343 filed Sept. 22, 1975 now U.S. Pat. No. 4,119,143.

BACKGROUND OF THE INVENTION

As the resources of combustible fuels to supply energy for heating,cooling and electricity are becoming more depleted, considerableinterest has been generated in the use of solar energy to satisfy theserequirements. The ability of a solar powered system to effectivelyutilize solar energy in a reliable and economical manner depends inlarge part on (1) its ability to efficiently store large quantities ofheat during the limited number of hours of available sunlight in orderto operate the system during the time in which sunlight is notavailable; and (2) its ability to efficiently store heat at the highestpossible temperature over a relatively wide range of collectiontemperatures during the available hours of sunlight.

Because water has proved to be one of the most economical storagemediums available from the present state of the art, most prior artsolar energy storage systems use water as the storage medium. Since theamount of heat that can be stored in a fixed quantity of water isdirectly proportional to its temperature, it is desirable to have thewater at the highest temperature possible in order to keep the quantityof water required for storage at a minimum. On the other hand, because asingle hot water storage tank can absorb heat only when the temperaturefrom the solar collector is higher than the temperature of the water inthe storage tank and because the available temperature at the solarcollector varies significantly over the normal hours of availablesunlight, it is desirable to use multiple storage tanks which permitshifting the heat storage to another tank when one of the tanks will notabsorb any more heat from the solar collector.

Multiple water storage tank systems have been proposed where the solarcollector is connected to the appropriate storage tank throughtemperature controlled mechanical valves. These systems require thatboth the temperature of the heat output from the solar collector and thetemperatures of the water in the tanks be sensed, and that anappropriate control system be provided so that the mechanical valves canbe sequenced to transfer the solar collector heat output from onestorage tank as its temperature approaches that of the output from thesolar collector to another storage tank which will accept the heatoutput. This has necessarily required these systems to be complex andthus expensive to build and operate. Similar systems have been proposedwhich provide for the recovery of usable heat from these storage tanks,however, such heat recovery systems have suffered from the samedrawbacks as the prior art storage systems.

SUMMARY OF THE INVENTION

These and other problems and disadvantages associated with the prior artare overcome by the invention disclosed herein by providing a heattransfer link that connects the heat output from a heat source such as asolar collector to a heat sink capable of receiving heat such as a heatstorage tank which allows rapid transfer of large quantities of heatfrom the heat output of the solar collector to the heat storage tank aslong as the heat output from the solar collector is slightly higher thanthe temperature of the heat storage tank but substantially prevents theflow of heat from the storage tank back into the solar collector whenthe temperature of the storage tank is substantially equal or higherthan the temperature of the solar collector. The heat transfer link actsas a heat check valve to allow the heat from the heat source to flowinto the heat sink but prevents the reverse flow of heat from the heatsink back into the heat source. Various combinations of these heattransfer links can be used to provide a multiple storage tank systemwith the capability of storing heat at different temperatures withoutthe use of temperature sensors, mechanical valves or control systems.

A similar heat transfer link can be used to provide a heat recoverysystem from the heat storage tanks. By using various combinations ofthese heat transfer links, a heat recovery system for recovering heatfrom multiple heat storage tanks at different temperatures can beprovided without the use of temperature sensors, mechanical valves orcontrol systems.

The heat transfer link of the invention is adapted to transfer heat froma source of heat to a heat sink while substantially preventing thetransfer of heat from the heat sink back to the source of heat. The heattransfer link includes a first heat exchange means carrying a workingfluid with a prescribed vaporization temperature and pressure rangewhere the first heat exchange means is located at a first elevation andplaces the working fluid therein in a heat exchange relationship withthe heat output of the source of heat to vaporize the working fluid. Theheat transfer link also includes a second heat exchange means located ata second elevation higher than the first elevation and connected to thefirst heat exchange means for receiving the vaporized working fluid fromthe first heat exchange means and returning condensed working fluid tothe first heat exchange means under the force of gravity. The secondheat exchange means places the vaporized working fluid in a heatexchange relationship with the heat sink so that the heat sink willabsorb the heat from the vaporized working fluid to condense it as longas the temperature of the heat sink is below the temperature of thesource of heat. As the vaporized working fluid condenses, the condensedworking fluid flows back to the first heat exchanger means under theforce of gravity to be re-vaporized.

For a heat storage system, the source of heat may be the heat output ofthe solar collector and the heat sink may be a plurality of storagetanks, usually filled with water. For a heat recovery system, the sourceof heat is usually the plurality of storage tanks, usually filled withwater, while the heat sink is usually a heating system, a heat drivencooling system or some other heat driven system.

For a heat storage system, if the heated output from the heat source isserially through multiple heat transfer links individually connected tomultiple heat storage tanks, then the first most upstream tank will beheated first followed successively by the downstream tanks. If a singleheat transfer link is used with series connected output heat exchangesindividually associated with multiple heat storage tanks, substantiallythe same result can be achieved.

For a heat recovery system using multiple heat storage tanks, if theoperating fluid of the heat sink is passed serially through multipleheat transfer links individually connected to the storage tanks so thatthe lowest temperature tank is the most upstream, then the highesttemperature can be maintained in the operating fluid for the longestperiod of time. If a single heat transfer link is used with seriesconnected input heat exchangers individually associated with multipleheat storage tanks, the heat may be sequentially recovered from thestorage tanks starting with either the highest or lowest temperaturetank first.

These and other features and advantages of the invention will becomemore apparent upon consideration of the following specification andaccompanying drawings wherein like characters of reference designatecorresponding parts throughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating one of the heat transferlinks of the invention;

FIG. 2 is a saturated pressure-enthalpy curve for a typical refrigerant;

FIG. 3 is a schematic drawing illustrating one embodiment of a heatstorage and recovery system of the invention;

FIG. 4 is a schematic drawing illustrating another embodiment of a heatstorage and recovery system of the invention; and,

FIG. 5 is a schematic drawing illustrating still another heat recoverysystem of the invention.

These figures and the following detailed description disclose specificembodiments of the invention, however, it is to be understood that theinventive concept is not limited thereto since it may be embodied inother forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1, the heat transfer link 10 is connected between aheat source 11 and a heat sink 12 and is in a heat exchange relationshipwith both. The heat transfer link 10 operates to transfer heat from theheat source 11 to the heat sink 12 but prevents the transfer of heatfrom the heat sink 12 back to the heat source 11. Thus, the heattransfer link 10 is a one direction heat transfer device as will becomemore apparent.

The heat transfer link 10 comprises an input heat exchanger 15 includinga fluid reservoir 16 with an upper end 17. The fluid reservoir 16 ischarged wtih a working fluid 18 which has a prescribed vaporizationtemperature and pressure relationship so that the liquid level of theworking fluid has elevation E₁. While a number of different workingfluids may be used as long as the working fluid can be vaporized at theminimum operating temperature of the heat source 11, refrigerantsnormally used in air conditioning systems such as Refrigerant 12 havebeen found satisfactory when heat is being received from a solarcollector, especially where the heat source working fluid is water andthe heat sink working fluid is water. The input heat exchanger 15 placesthe working fluid 18 in a heat exchanger relationship with the heatoutput of the heat source 11 so that the working fluid in reservoir 16will be vaporized when the temperature of the heat output from the heatsource 11 exceeds the vaporization temperature of the working fluid aswill become more apparent.

The heat transfer link 10 also includes an output heat exchanger 20which has an upper end 21 and a lower end 22. The output heat exchanger20 defines a heat transfer chamber 24 therein which receives thevaporized working fluid 18 therein and places this vaporized workingfluid in a heat exchange relationship with the heat sink 12. The lowerend 22 of the output heat exchanger 20 is located at a second elevationE₂ higher than the first elevation and the lower end 22 of the heattransfer chamber 24 in output heat exchanger 20 is connected throughtransfer pipe 25 to the upper end 17 of the fluid reservoir 16 in inputheat exchanger 15. The upper end 21 of the heat transfer chamber 24 inoutput heat exchanger 20 is closed. The fluid chamber 16, the pipe 25,and the heat transfer chamber 24 define a closed system and this systemis charged with working fluid 18 so that pipe 25 and chamber 24 arefilled with vaporized working fluid when no heat is being transferredfrom input heat exchanger 15 to output heat exchanger 20.

In operation, the fluid chamber 16, the pipe 25 and the heat transferchamber 24 are charged with the working fluid 18 at a prescribedpressure when the temperature of the working fluid is at a knowntemperature. The initial charging pressure is selected to cause theworking fluid 18 in the input heat exchanger 15 to start boiling tovaporize the liquid working fluid when the available temperature fromthe heat source 11 rises above a prescribed value to start the operationof the heat transfer link 10.

Assuming initially that the temperature T_(i) of the heat source 11 isthe same as the temperature T_(o) of the heat sink 12, the working fluid18 in a liquid state will partly fill the reservoir 16 in the input heatexchanger 15. The rest of reservoir 16, the pipe 25 and the heattransfer chamber 24 will be filled with the workding fluid 18 in a vaporstate. The temperature T ₁ and pressure P₁ of the liquid and vapor ofthe working fluid 18 will be substantially constant throughout both heatexchangers 15 and 20 and the pipe 25. The temperature T₁ will be equalto temperatures T_(i) and T_(o) and the vapor phase of working fluid 18will be in equilibrium with the liquid phase thereof. Because there areno temperature differences between the heat source 11 and heat sink 12,no heat will be transferred and the system will be at a steady state.When the output temperature T_(i) of the heat source 11 rises totemperature T_(i) ' above the temperature T_(o) of the heat sink 12, theworking fluid 18 in its liquid phase will start to boil. This causes theworking fluid 18 to absorb heat and increase its enthalpy. Thus, theheat source 11 is now trying to drive the temperature T ₁ of the workingfluid 18 toward the higher temperature T_(i) ' of the heat source 11 byvaporizing liquid working fluid while the heat sink 12 is trying todrive the temperature T₁ toward the lower temperature T _(o) of the heatsink 12 by condensing vapor working fluid. This generates a slightpressure difference in the vapor working fluid 18 between exchanger 15and exchanger 20 so that a net vapor flow is generated between theexchangers 15 and 20 driving the vapor and thus the heat energy towardexchange 20. The temperature of the working fluid 18 will rise to ahigher temperature T₁ ' with a corresponding rise in pressure topressure P₁ ' where the liquid and vapor phases again reach equilibriumbut the pressure and temperature will still be virtually constantthroughout the system.

The temperature T_(o) of the heat sink 12 is now below the temperatureT₁ ' of the working fluid vapor in the output heat exchanger 20 so thatthe latent heat in working fluid 18 is transferred to the heat sink 12to decrease the enthalpy of the working fluid vapor causing it to startto condense to its liquid phase. Because the liquid working fluid 18 inthe output heat exchanger 20 is at substantially the same temperature T₁' as the vaporized working fluid 18, virtually no heat transfer takesplace between the liquid and vapor as the condensed liquid working fluid18 flows back by gravity to the input heat exchanger 15 through pipe 25.As the vapor in the output heat exchanger 20 is condensed, more of theliquid in the input heat exchanger 15 is vaporized to replace thecondensed vapor. Thus, it will be seen that heat will be continuouslytransferred from the output of the heat source 11 to the working fluid18 through the input heat exchanger 15 while heat will be continuouslytransferred from the working fluid 18 to the heat sink 12 through theoutput heat exchanger 20 as long as the actual temperature T_(o) ^(a) ofthe heat sink 12 remains below the temperature T_(i) ' of the output ofthe heat source 11. The heat transfer rate from the heat source 11 tothe heat sink 12 through the heat transfer link 10 is, of course,proportional to the temperature difference between the heat source 11and heat sink 12 with greater temperature differences producing greaterheat transfer rates. Because the latent heat of the working fluid 18 isused as the heat transfer mechanism, the heat transfer rate capabilityof link 10 is several times greater than a heat transfer mechanism thatdoes not use vaporization and condensation.

Reference to FIG. 2, which is a saturation pressure-enthalpy curve for atypical refrigerant such as Refrigerant 12 (Freon-12, a trademark ofDuPont de Nemours Co.), will better explain the pressure and temperaturerelationships of the heat transfer. Because the working fluid 18 changesfrom its liquid to its vapor phase and back to its liquid phase at asubstantially constant pressure and temperature under saturationconditions, it will be seen that heat is transferred while the workingfluid 18 remains at a substantially constant temperature. For instance,assume that heat is being transferred into the heat transfer link fromthe heat source and the equilibrium temperature of the working fluid inthe link is 100° F. The heat being transferred into and out of the linkworking fluid is represented by the solid line A in FIG. 2 extendingbetween the point P_(L) on the saturated liquid side of the curve andP_(v) on the saturated vapor side of the curve. Now, suppose thetemperature of the heat source imposed on the heat transfer link isincreased. This raises the equilibrium temperature of the working fluidin the link to 140° F. as an example. The heat being transferred intoand out of the link working fluid is now represented by dashed line Bextending between P_(L) ' on the saturated liquid side of the curve andpoint P_(v) ' on the saturated vapor side of the curve. As thetemperature of the heat source rises, it will be seen that both thepressure and temperature of the working fluid 18 rise, however, thehigher pressure and temperature are substantially constant throughoutthe working fluid 18.

When the temperature T_(o) of the heat sink 12 equals the temperature T_(i) of the heat source 11 or the temperature T_(i) of the heat source11falls below the temperature T_(o) of the heat sink 12 as would occurwith a solar collector heat source over a period of daily operation, theliquid working fluid 18 in the input heat exchanger 15 would no longerbe vaporized since the pressure of the vapor working fluid 18 would beequal to or greater than the equilibrium vapor pressure of the liquidworking fluid 18 in the input heat exchanger 15. All of the condensedliquid working fluid 18 will now drain back into the input heatexchanger 15 and not vaporize. When the temperature T_(i) reduces to avalue less than temperature T_(o), some of the vapor working fluid 18will condense until a new lower equilibrium pressure is reached.However, since there is now no liquid working fluid 18 in the outputheat exchanger 20, the higher temperature T_(o) in the heat sink 12 canproduce no vapor in the working fluid 18 and there will consequently beno heat transferred through the working fluid 18 in the reversedirection from the heat sink 12 to the heat source 11 except for a smallamount of heat flow caused by conduction through pipe 25 and byconvection through the vapor working fluid 18 in pipe 25. Thus, the heattransfer link 10 effectively transfers heat only from the heat source 11to the heat sink 12 and not in the reverse direction.

FIRST EMBODIMENT OF HEAT STORAGE AND RECOVERY SYSTEM

FIG. 3 illustrates a heat storage and recovery system 100 which uses aplurality of heat transfer links to store and recover heat at differenttemperature levels. This system is especially adaptable to store heatfrom a solar collector SC that acts as the heat source for the storageloop 101 of the system. The solar collector SC has a heated fluidoutput, usually water, whose heat is transferred to a plurality ofinsulated storage tanks ST with a storage fluid therein, usually water.These storage tanks ST act as the heat source in the heat recovery loop102 of the system. The heat in the storage tanks ST is transferred to aheat driven system HDS such as a heater or heat driven air conditionerto drive the system. While different numbers of storage tanks ST may beused, three are illustrated and individually designated ST₁, ST₂ andST₃.

The system heat input loop 101 includes a separate storage heat transferlink 110 transferring heat from the output fluid of the solar collectorSC to one of the storage tanks ST. The heat transfer links areindividually numbered 110₁, 110₂ and 110₃ to correspond to the storagetank into which each transfers heat from the solar collector. Since eachof the storage heat transfer links 110 have the same construction, onlylink 110₁ will be described in detail with corresponding referencenumbers being applied to links 110₂ and 110₃.

The input heat exchanger 115₁ of link 110₁ is a shell and tube type heatexchanger where the working fluid 118₁ of the link is carried in theshell chamber 116₁ while the heated fluid output from the solarcollector SC passes through the tubes 113₁ of exchanger 115₁ to heat theworking fluid 118₁. The output heat exchanger 120₁ is a coil verticallyoriented and immersed in the storage fluid in tank ST₁. The passage 124₁in coil 120₁ is closed at its upper end 121₁ while its lower end 122₁ isconnected to the vapor space in the shell of heat exchanger 115₁ throughthe transfer pipe 125₁. It will thus be seen that the link 110₁ willtransfer heat from the heated fluid output from the solar collector SCpassing through tube 113, to the storage fluid in tank ST₁ in the mannerdescribed for link 10 but will not transfer significant heat in thereverse direction from the storage fluid in the storage tank to thefluid output from the solar collector. The level of the liquid workingfluid in the shell chamber 116₁ is at the lower elevation E_(1i) whilethe lower end 122₁ of coil 120 is located at the higher elevation E_(1o)so that the working fluid 118₁ condensed in coil 120₁ will flow back tothe shell chamber 116₁ in exchanger 115₁ through pipe 125₁ under theinfluence of gravity. Normally, the pipe 125₁ will be insulated.

It will be noted that the heated fluid output from the solar collectorSC passes serially through the tubes 113₁, 113₂ and 113₃ of the heatexchangers 115₁, 115₂ and 115₃ of the heat transfer links 110₁, 110₂ and110₃. Thus, the heated fluid output from solar collector SC passesthrough the tube 113₁ in link 110₁ first, then through tube 113₂ in link110₂, and finally through the tube 113₃ in link 110₃ before it isrecycled through the solar collector SC for reheating.

The system heat input loop 101 of the system 100 operates with thetransfer links 110₁ -110₃ each transferring heat to its associatedstorage tank under the theory of operation described hereinabove forlink 10. Assuming that the storage tank ST₁ is at an initial temperatureT₁, that the storage tank ST₂ is at an initial temperature T₂ and thatthe storage tank ST₃ is at an initial temperature T₃, the systemoperation will be described where the input temperature T_(i) from thesolar collector heat source SC is at a higher temperature of any of thetanks ST. The heated fluid output from the solar collector SC passesfirst through the tube 113₁ in the input heat exchanger 115₁ of thefirst heat transfer link 110₁ where the working fluid 118₁ in the heattransfer link 110₁ is vaporized thereby absorbing heat and transferingheat from the heated fluid output of collector SC to the storage tankST₁. This causes the heated fluid output from the solar collector SC tobe cooled to a new lower temperature T_(i) ' by the time it passes tothe next heat transfer link 110₂. If this new temperature T_(i) ' ishigher than the temperature T₂ of the storage tank ST₂, then heat willalso be transferred through the heat transfer link 110₂ to cool theheated fluid output from the colar collector SC to a still lowertemperature T_(i) " by the time it passes to the third heat transferlink 110₃. If the temperature T_(i) " is higher than the temperature T₃in the storage tank ST₃, then additional heat will be transferred intothe storage tank ST₃ before the fluid output from the colar collector SCfinally is recycled back through the solar collector SC to be reheated.The rate of heat transferred into each tank ST₁ -ST₃ is, of course,proportional to the temperature difference between the temperature ofthe fluid in the tank and the temperature of the fluid output from thesolar collector while it is passing through the particular heat transferlink associated with the tank. Thus, it will be seen that thetemperature T₁ in the tank ST₁ will be driven toward the outputtemperature T_(i) from the solar collector with the temperatures of eachof the subsequent tanks ST₂ and ST₃ being at lower temperatures. As thetemperature T₁ of tank ST₁ is driven toward the temperature T_(i), moreand more of the heat transferred out of the heat source output fluidwill shift to the next downstream storage tank since the heattransferred is proportional to the temperature differences. If thetemperature T₁ reaches the temperature T_(i), then the fluid output fromthe solar collector SC will pass through link 110.sub. 1 without heattransfer because of the one way action of link 110₁ and the heat will betransferred into the next downstream tank which is at a temperaturelower than the temperature of the fluid output from the solar collector.

Because the available solar heat at any given location varies during thehours of daily sunlight, the output temperature T_(i) from the solarcollector SC may drop below the temperature T₁ in the storage tank ST₁while the temperature will still remain higher than the temperature T₂or T₃ in tanks ST₂ or ST₃. Because of the one way action of each of theheat transfer links 110, the heated fluid output from the solarcollection SC will pass through those heat transfer links associatedwith the storage tanks ST at a temperature higher than the temperatureT_(i) without transferring heat to the particular storage tank. As soonas this heated fluid output reaches the heat transfer link 110associated with the upstreammost storage tank ST at a lower temperaturethan the temperature T_(i), heat will be transferred through the heattransfer link 110 into the storage tank ST until the temperature of thestorage fluid in that particular storage tank rises to or exceeds thetemperature T_(i). Normally the temperature T₁ will be greater than thetemperature T₂ and the temperature T₂ will be greater than thetemperature T₃. If the temperature T_(i) falls below all of thetemperatures at the storage tanks, the fluid output from the solarcollector will flow through all of the input heat exchangers 115 withoutheat being transferred to any of the associated storage tanks ST. Whenthe input temperature T_(i) again rises above any of the temperatures ofthe storage fluids in the storage tanks, heat will be transferredthrough the associated link 110 into the storage fluid in the mostupstream storage tank whose temperature is below the temperature T_(i).

The heat recovery loop 102 includes a separate recovery heat transferlink 210 connecting each storage tank with the driving fluid of a heatdriven system HDS. The recovery heat transfer links 210 are individuallynumbered 210₁, 210₂ and 210₃ to correspond to the storage tank eachconnects to the driving fluid of the heat driven system HDS. Since eachof the recovery heat transfer links 210 have the same construction, onlylink 210₁ will be described in detail with corresponding referencenumbers being applied to links 210₂ and 210₃.

The input heat exchanger 215₁ of link 210₁ is a coil vertically orientedand immersed in the storage fluid in tank ST₁. The working fluid 218₁ ofthe link is carried in the coil passage 216₁ which is closed at itslower end while its upper end is connected to the output heat exchanger220₁ through the transfer pipe 225₁. The output heat exchanger 220₁ is ashell and tube type heat exchanger where the vaporized working fluid218₁ is received in the shell chamber 224₁ while the heat driven systemdriving fluid to be heated passes through the tube 221₁ of the exchanger220₁. It will further be noted that the upper end of the input heatexchanger 215₁ is located at a first elevation E_(1i) while thelowermost portion of the shell chamber 224₁ is located at a higherelevation E_(1o). It will further be noted that the liquid level of theworking fluid 218₁ substantially fills the coil passage 216₁ underequilibrium conditions. It will thus be seen that the link 210₁ willtransfer heat from the storage liquid in tank ST₁ to the heat drivensystem driving fluid passing through the tube 221₁ in the output heatexchanger 220₁ in the manner described for the link 10 but will nottransfer significant heat in the reverse direction from the heat drivensystem driving fluid passing through heat exchanger 220₁ to the storagefluid in the storage tank ST₁. In essence, it will be seen that thelinks 210 are simply the links 110 turned upside down. Thus, the inputheat exchangers 215 will vaporize the working fluids 210 and the shelland tube type heat exchangers 220 will condense the working fluids 218.

It will further be noted that the driving fluid to be heated passesserially through the heat transfer links 210₁, 210₂ and 210₃. Dependingon the size of the heat exchangers 215, the driving fluid to be heatedwill tend to be heated to the highest temperature available from thestorage tanks ST. If the driving fluid to be heated is passed seriallythrough the recovery heat transfer links 210 as seen in FIG. 3 so thatthe driving fluid passes first through the output heat exchanger 220₃ ofthe heat transfer link 210₃, and assuming that the temperature T₃ isless than the temperature T₂ and the temperature T₂ is less than thetemperature T₁, then heat will be transferred from each of the storagetanks ST but the temperature of all of the tanks ST will be lowered atthe same time. Assuming that the inlet temperature of the driving fluidis at T_(e) seen in FIG. 3, then the storage heat transfer link 210₃will transfer heat from the storage tank ST₃ into the driving fluid toraise the temperature of the driving fluid to the temperature T_(f) bythe time it passes through the link 210₃. If the temperature T₂ in tankST₂ is higher than the temperature T_(f), then additional heat will betransferred from the storage tank ST₂ into the driving fluid as itpasses through the output heat exchanger 220 of the link 210₂. Thisserves to raise the temperature of the driving fluid to a still highertemperature T_(g) by the time it passes through the link 210₂, and, ifthe temperature T₁ is higher than the temperature T_(g), then the heattransfer link 210₁ will transfer additional heat into the driving fluidas it passes through the link 210₁ to raise its temperature to a highertemperature T_(h). This output temperature T_(h) of the driving fluidwill approach that of the highest temperature stored or temperature T₁.On the other hand, if the flow of the heat driven system driving fluidthrough the heat transfer links 210 is reversed so that the drivingfluid flows first through the heat transfer link 210₁ associated withthe highest temperature T₁ in the storage tanks ST, and the effectiveheat transfer surface area of the heat exchanger 215₁ of the link 210₁is sufficiently large, then the driving fluid will be heated to atemperature approaching the temperature T₁ before it exits the heatexchanger 215₁. If the temperature T₁ is greater than the temperature T₂and the temperature T₃, then the temperature of the driving fluid as itexits the link 210₁ will be higher than the temperatures T₂ and T₃ sothat substantially no heat will be transferred from the storage tanksST₂ and ST₃ until the temperature T₁ drops to the vicinity of thetemperature T₂ or T₃ whereupon the heat transfer links 210₂ and/or 210₃will start to transfer heat into the driving fluid. If any one of thetemperatures T₁, T₂ or T₃ drops below the initial temperature of theheat driven system driving fluid passing through its associated heattransfer link 210, then no heat will be removed from the associatedlower temperature storage tank ST.

The recovery loop 102 is well suited to heat recovery where it isdesirable to recover heat at the highest possible temperature for thelongest period of time. A number of applications would use this approachsuch as, for example, where the heat driven system uses an absorptionrefrigeration cycle which requires temperatures greater than about 180°F.

SECOND EMBODIMENT OF HEAT STORAGE AND RECOVERY SYSTEM

FIG. 4 illustrates another heat storage and recovery system 300 whichuses a modified heat transfer link construction to store and recoverheat at different temperature levels. This system, like system 100, isespecially adaptable to store heat from a solar collector SC that actsas the heat source for the heat input loop 301 of the system. The solarcollector SC has a heated fluid output, usually water, whose heat istransferred to a plurality of insulated storage tanks ST with a storagefluid therein, usually water.These storage tanks ST act as the heatsource in the heat recovery loop 302 of the system. The heat in thestorage tanks ST is transferred to a heat driven device HDD such as aheater or heat driven air conditioner to drive the device. Whiledifferent numbers of storage tanks ST may be used, three are illustratedand individually designated ST₁, ST₂ and ST₃.

The heat from the heated fluid output of solar collector SC istransferred to the storage fluid in the storage tanks ST by acombination storage heat transfer link 310 whose theory of operation isbased on that of link 10. The storage heat transfer link 310 has asingle input heat exchanger 315 and a plurality of output heatexchangers 320 serially connected to the input heat exchanger 315. Theheat exchanger 315 is a shell and tube type heat exchanger where theworking fluid 318 of the link is carried in the shell chamber 316 whilethe heated fluid output from the solar collector SC passes through thetube 313 of exchanger 315 to heat the working fluid 318. The workingfluid liquid level in the shell chamber 316 is at elevation E_(o). Eachof the output heat exchangers 320 is a coil vertically oriented andimmersed in the storage fluid of one of the storage tanks ST. For sakeof simplicity, the coils have been numbered 320₁, 320₂ and 320₃corresponding to the storage tank number in which they are submerged.Thus, it will be seen that coil 320₁ defines a passage 324₁ therein withan upper inlet end 321₁ and a lower outlet end 322₁. Likewise, coil 320₂has passage 324₂, inlet end 321₂ and outlet end 322₂ ; and coil 320₃ haspassage 324₃, inlet end 321₃ and outlet end 322₃. The upper inlet end321₁ of coil 320 is located in tank ST₁ at an elevation E_(1i) higherthan elevation E_(o) and is connected to the vapor space in the shellchamber 316 in heat exchanger 315 through the transfer pipe 325. Thelower outlet end 322₁ of coil 320₁ is located at elevation E_(1o) whichis lower than elevation E_(1i) but higher than elevation E_(o). Theupper inlet end 321₂ of coil 320₂ in tank ST₂ is located at elevationE_(2i) at least as low as elevation E_(1o) but higher than elevationE_(o) and is connected to the outlet end 322₁ of coil 320₁ throughtransfer pipe 326. The lower outlet end 322₂ of coil 320₂ is located atelevation E_(2o) lower than elevation E_(2i) but higher than elevationE_(o). In like manner, the upper inlet end 321₃ of coil 320₃ in tank ST₃is located at elevation E_(3i) at least as low as elevation E_(2o) buthigher than elevation E_(o) and is connected to the outlet end 322₂ ofcoil 320₂ by transfer pipe 328. The lower outlet end 322₃ of coil 320₃is located at elevation E_(3o) lower than elevation E_(3i) but higherthan elevation E_(o) and is connected back to the shell chamber 316 ininput heat exchanger 315 therein through return pipe 329 and meteringvalve 330. Thus, it will be seen that the vapor working fluid 318 cansuccessively circulate through the coils 320₁ -320₃ while working fluid318 condensed in the coils 320₁ -320₃ drains back to the exchanger 315through the succeeding coils and valve 330.

Assuming an initial temperature T₁ in tank ST₁, a temperature T₂ in tankST₂ and a temperature T₃ in tank ST₃, a temperature T_(i) in the heatedfluid output of solar collector SC higher than temperatures T₁ -T₃ willcause the liquid working fluid 318 in heat exchanger 315 to startvaporizing and absorbing heat as the solar collector fluid output passesthrough exchanger 315. This starts vapor working fluid 318 circulatingout through pipe 325 and serially through coils 320₁ -320₃. As soon asthe temperature of the vapor working fluid 318 in coil 320₁ rises abovetemperature T₁, it starts to condense and drain back to exchanger 315through coils 320₂ and 320₃ and valve 330. While the vapor working fluid318 may initially condense in all three coils, the valve 330 which is anadjustable flow control valve is adjusted to control the flow ofcondensed liquid working fluid 318 back to exchanger 315 so that theliquid level of the working fluid 318 in coils 320₁ -320₃ will bemaintained at the outlet end of the particular coil 320₁ -320₃transferring heat into the storage tank associated therewith across someprescribed temperature difference between the working fluid 318 and thestorage fluid receiving heat. Therefore, in this instance, anappropriate adjustment of valve 330 will cause the condensed liquidlevel of fluid 318 to rise to the level of the outlet end 322₁ of coil320₁ as indicated at point P₁ in FIG. 4 when the system reaches steadystate conditions. Because coils 320₂ and 320₃ are now filled with liquidworking fluid 318, the heat transferred to tanks ST₂ and ST₃ will besmall compared to the heat transferred to tank ST₁. When temperature T₁substantially equals the temperature T_(i) or temperature T_(i) dropsbelow temperature T₁, the vapor working fluid 318 will cease to becondensed in coil 320₁ and the level of condensed working fluid 318 incoils 320₂ and 320₃ will start to lower since this condensed workingfluid continues to drain back to heat exchanger 315 through valve 330.The level of the condensed liquid working fluid 318 lowers to a newposition P₂ at coil 320₂ so that coil 320₂ now condenses the workingfluid 318 to maintain the level of the condensed working fluid until thetemperature T₂ substantially equals temperature T_(i) or temperatureT_(i) drops below temperature T₂. The level of condensed working fluidthen lowers to a new position P₃ where the vapor working fluid 318 iscondensed in coil 320₃. Normally, then, the temperature T₁ will behigher than temperature T₂ and temperature T₂ will be higher thantemperature T₃. It will also be noted that the transition of thecondensing of the working fluid 318 from one coil 320 to the next lowertemperature coil 320 is a gradual process so that some condensation willprobably be occurring in two of the coils 320 at the same time duringthe transition period. It is also to be understood that the heat inputloop 301 will work as long as all of the coils 320₁ -320₃ are higherthan the elevation E_(o), coil 320₂ is no higher than coil 320₁ and coil320₃ is no higher than coil 320₂.

In the heat recovery loop 302, heat is transferred to the driving fluidof the heat driven device HDD from the storage tanks ST by a combinationrecovery heat transfer link 410 whose theory of operation is also basedon that of link 10. The loop 302 uses the lowest temperature tank first.

The recovery heat transfer link 410 has a plurality of input heatexchangers 415, one being associated with each storage tank ST. Theseinput heat exchangers 415 have been numbered 415₁, 415₂ and 415₃ tocorrespond to the numbering of tanks ST₁, ST₂ and ST₃ and are seriallyconnected to each other. The heat exchangers 415 are coils with the coil415, in tank ST₁ having fluid passage 424₁ with inlet 421₁ and outlet422₁. The outlet 422₁ is located at elevation E_(1o) which is thehighest elevation of coil 415₁. The coil 415₂ in tank ST₂ has fluidpassage 424₂ with inlet 421₂ and outlet 422₂, the outlet 422₂ beinglocated at elevation E_(2o), the highest elevation of coil 415₂, andconnected to the inlet 421₁ of coil 415₁ by transfer pipe 425. The coil415₃ in tank ST₃ has fluid passage 424₃ with inlet 421₃ and outlet 422₃which is located at elevation E_(3o), the highest elevation of coil415₃. Outlet 422₃ of coil 415₃ is connected to inlet 421₂ of coil 415₂by transfer pipe 426. The recovery loop 302 also includes a fluidreceiver 428 defining a fluid chamber 429 therein with an upper inlet430 and lower outlet 431. The outlet 431 is located at elevation E_(Ro)higher than any of the elevations E_(1o), E_(2o) or E_(3o) and isconnected to the inlet 421₃ of coil 415₃ through metering valve 432 andinlet pipe 434. The inlet 430 has an elevation E_(Ri) higher thanelevation E_(Ro). The output heat exchanger 420 is a coil which definesa passage 435 therethrough with inlet 436 and outlet 438. Outlet 438 hasan elevation E_(o) higher than the elevation E_(Ri) of receiver 429 andis connected to the inlet 430 so that as vapor working fluid 418 in loop302 condenses in coil 420, the condensed working fluid flows into thechamber 429 in receiver 428. The inlet 436 to coil 420 is located atelevation E_(i) which is higher than elevation E_(o) and is connected tothe outlet 422₁ of coil 415₁ through vapor pipe 439. The coil 420 may belocated in a duct D in a heating system so that air can be forced acrosscoil 420 by fan F to heat the air while coiling coil 420.

The operation of the heat recovery loop 302 can best be described bystarting with the working fluid 418 in its liquid phase in the fluidchamber 429 of receiver 428. The metering valve 432 is adjusted so thatthe liquid working fluid 418 is allowed to flow by gravity into the coil415₃. If the initial temperature T_(o) of the working fluid 418 inreceiver 428 is below the temperature T₃ in the storage tank ST₃, thenthe liquid working fluid 418 will be vaporized in coil 415₃ therebyabsorbing heat from the tank ST₃. This causes the vaporized workingfluid 418 to flow out of coil 415₃ through coil 415₂ and coil 415₁ andsubsequently through the vapor pipe 439 to the output heat exchangercoil 420. If the temperature T_(a) of the air flowing through the duct Dis lower than the temperature T₃, then the vaporized working fluid 418will be condensed in the coil 420 and the condensed working fluid willflow back into the receiver 428 under the influence of gravity. It willbe noted that the vaporized working fluid 418 generated in the coil 415₃will absorb a small amount of heat to super heat the vapor as it flowsthrough coil 415₂ and will do likewise as the vapor working fluid 418passes through coil 415₁ since the temperature T₂ is higher thantemperature T₃ and the temperature T₁ is higher than the temperature T₂.The quantity of heat absorbed from the storage tanks ST₂ and ST₁ assuper heat, however, is small compared to the heat absorbed from thetank ST₃ because the heat absorbed by the working fluid 418 in coil 415₃is the latent heat of vaporization.

As heat is absorbed from the tank ST₃ by working fluid 418, thetemperature T₃ of the tank ST₃ continues to drop until such time as theavailable heat from the storage fluid in the tank ST₃ is not capable ofvaporizing all of the liquid entering the coil 415₃. At this time, thecoil 415₃ starts to fill with liquid working fluid 418 until some ofthis liquid working fluid overflows into the coil 415₂ where itvaporizes at the higher temperature T₂ of tank ST₂. The vaporizedworking fluid continues to flow through the coil 415₁ where it absorbsthe small amount of additional heat as super heat as it passes throughthe coil 415₁. The vapor working fluid 418 continues to flow to the coil420 where it is condensed and flows by gravity back into the receiver428. As indicated above, the temperature in the tank ST₂ will now startto drop and will reach a point where it can no longer vaporize all ofthe available liquid working fluid in the coil 415₂. Consequently, theliquid working fluid 418 will start filling the coil 415₂ and start toflow over into the coil 415₁ where the higher temperature T₁ willvaporize the liquid working fluid 418. This process continues until thetemperature T₁ in the tank ST₁ falls below the vaporizing temperature ofthe working fluid 418. Thus, it will be seen that the working fluid 418will be vaporized in the first coil 415 it sees which is at atemperature higher than the vaporizing temperature of the working fluid418. The heat recovery loop 302, then, uses the lowest usefultemperature first. This type heat recovery is, in many cases, the mostdesirable since it is easier to replace the lowest temperature heat inthe tanks ST by the solar collector SC, especially where the highestavailable temperature is not required in the coil 420 to drive the heatdrive system associated therewith. On the other hand, reversal of theorder of the coil 415 will cause the heat driving capability of thehighest temperature storage tank ST to be depleted first.

THIRD EMBODIMENT OF HEAT RECOVERY SYSTEM

FIG. 5 illustrates an alternate embodiment of the heat recovery loop andis designated by the numeral 500. This loop uses a modified heattransfer link construction to recover heat from storage tanks ST atdifferent temperature levels. The storage tanks ST act as the heatsource for the system and the heat stored in the storage tanks ST istransferred to a heat driven device HDD such as a heater or heat drivenair conditioner to drive the device. While different numbers of storagetanks ST may be used, three are illustrated and individually designatedST₁, ST₂ and ST₃. For the sake of clarity, the temperature T₁ of thetank ST₁ is higher than the temperature of T₂ of the tank ST₂ and thetemperature T₂ of the tank ST₂ is higher than the temperature T₃ of thetank ST₃. The heat from the tanks ST is transferred to the driving fluidof the heat driven device HDD from the storage tanks ST by a combinationrecovery heat transfer link 510 whose theory of operation is based onthat of link 10. The loop 500 removes heat from the highest temperaturetank first.

The recovery heat transfer link 510 has a plurality of input heatexchangers 515, one being associated with each storage tank ST. Theseinput heat exchangers have been numbered 515₁, 515₂ and 515₃ tocorrespond to the number of tanks ST₁, ST₂ and ST₃. The heat exchangers515₁ -515₃ are serially connected to each other as will become moreapparent. The heat exchangers 515 are coils with the coil 515₁ in tankST₁ having fluid passage 524₁ with lower end 521₁ and upper end 522₁.The upper end 522₁ is located at elevation E_(1o) and lower end 521₁ islocated at elevation E_(1i) lower than elevation E_(1o). The coil 515₂in tank ST₂ has fluid passage 524₂ with lower end 521₂ and upper end522₂, the upper end 522₂ being located at elevation E_(2o) at least aslow as elevation E_(1i) and the lower end 521₂ being located atelevation E_(2i) lower than elevation E_(2o). The upper end 522₂ isconnected to the lower end 521₁ of coil 515₁ by transfer pipe 525. Thecoil 515₃ in tank ST₃ has fluid passage 524₃ with lower end 521₃ andupper end 522₃. Upper end 522₃ is located at elevation E_(3o) at leastas low as elevation E_(2i) and lower end 521₃ is located at elevationE_(3i) lower than elevation E_(3o). Upper end 522₃ of coil 515₃ isconnected to lower end 521₂ of coil 515₂ by transfer pipe 526 and lowerend 521₃ is closed. The recovery loop 500 also includes an output heatexchanger 520 through which the driving fluid of the heat driven deviceHDD passes to be heated. Output heat exchanger 520 is a shell and tubetype heat exchanger where the vaporized working fluid 518 is received inthe shell chamber 528 while the heat driven system driving fluid to beheated passes through the tube 529 of the exchanger 520. It will furtherbe noted that the lowermost portion of the shell chamber 528 is locatedat elevation E_(i) higher than the output elevation E_(1o) of coil 515₁.The inlet 530 to shell chamber 528 is located in the lowermost portionof chamber 528 and connected to the upper end 522₁ of coil 515₁ by pipe531.

As mentioned above, the loop 500 recovers heat from the highesttemperature available from tanks ST. This type recovery may be desirablein some cases such as in the opraation of a device using an absorptionrefrigeration cycle where temperatures greater than about 180° F. arerequired.

In operation, the coils 515 are charged with working fluid 518 so thatall of the coils 515 are filled to a level such that the liquid workingfluid 518 fills at least a large portion of the upper coil 515₁ when allof the heat storage tanks ST are at their maximum operatingtemperatures. Assuming that the temperature T₁ in tank ST₁ is higherthan the temperature T₃ in the tank ST₂ and temperature T₂ is higherthan the temperature T₃ in the tank ST₃, the equilibrium pressure andtemperature in the working fluid 518 will be set by the temperature T₁in the tank ST₁. This will cause the liquid working fluid 518 in coil515₁ to start being vaporized with heat being transferred into thevaporized working fluid 518 from the tank ST₁. Because the temperatureT₁ in tank ST₁ sets the equilibrium pressure and temperature in theworking fluid 518, the equilibrium temperature and pressure will beabove that at which the working fluid 518 in coils 515₂ and 515₃ will bevaporized. Assuming that the temperature T_(d) of the driving fluidpassing through the tube 529 in the exchanger 520 is lower than thetemperature T₁, heat will be transferred to the driving fluid to heat itwhile causing the vapor working fluid 518 in the coil 520 to becondensed whereupon it flows back down toward the coil 515₁ under theinfluence of gravity for revaporization. The temperature T₁ in the tankST₁ continues to drop as heat is taken from the tank and transferred tothe driving fluid until the temperature T₁ substantially equals thetemperature T₂ in the storage tank ST₂. At this point, the liquidworking fluid 518 in the coil 515₂ will start being vaporized and heatwill now be transferred from both tanks ST₁ and ST₂ essentially equallysince the evaporation of the working fluid 518 will take place all alongthe coil 515₁ and 515₂. A small temperature and pressure gradient willbe established between the outlet 522₁ af the coil 515₁ and the inlet521₂ of the coil 515₂ due to the effect of the weight of the column ofliquid working fluid 518 on the equilibrium pressure of the workingfluid. Heat will continue to be transferred from the tank ST₁ and ST₂until their temperatures substantially equal the temperature T₃whereupon evaporation will begin in the coil 515₃ and continue in thecoils 515₁ and 515₂. Heat will continue to be taken from all of thetanks ST so long as the temperatures in the tanks remain above thetemperature of the driving fluid passing through the tubes 529 in theexchanger 520. The loop 500 will finally stop functioning when thetemperature of the tanks ST reaches the temperature of the driving fluidpassing into the tubes 529 of the exchanger 520. It will be noted thatbecause the equilibrium pressures in the working fluid 518 are set bythe highest temperature storage tank ST, the loop 500 will operate toalways transfer heat from the highest temperature storage tank first,the next highest temperature storage tank next and finally the lowesttemperature storage tank. The same result may be achieved if the coils515₁ -515₃ are connected to output heat exchanger 520 in parallel.

The various embodiments of the heat storage loop and heat recovery loophave been described in specific configurations, however, it is to beunderstood that any one of the heat storage loops may be used with anyone of the heat recovery loops. This is because there is no positiveconnection between the heat storage loops and the heat recovery loops.

While specific embodiments of the invention have been disclosed herein,it is to be understood that full use may be used of modifications,substitutions and equivalents without departing from the scope of theinvented concept.

What is claimed as invention is:
 1. A heat transfer system comprising:afirst heat storage tank; a second heat storage tank; a first heatstorage fluid in said first heat storage tank; a second heat storagefluid in said second heat storage tank; a heat sink means for receivingheat including an operating fluid to be heated; a working fluid having aprescribed vaporization temperature and pressue range; an input heatexchange means including a first input heat exchanger and a second inputheat exchanger, said first input heat exchanger carrying said workingfluid therein in a heat exchange relationship with said first heatstorage fluid and located at a first input elevation, and said secondinput heat exchanger carrying said working fluid therein in a heatexchange relationship with said second heat storage fluid and located ata second input elevation; and an output heat exchange means includingfirst output heat exchanger and a second output heat exchanger, saidsecond output heat exchanger serially connected with said first outputheat exchanger to said heat sink means so that the operating fluid ofsaid heat sink means passes serially through said first and secondoutput heat exchangers, said first output heat exchanger located at afirst output elevation higher than said first input elevation and saidsecond output heat exchanger located at a second output elevation higherthan said second input elevation; said first input heat exchangeroperatively connected to said first output heat exchanger for placingthe vaporized working fluid from said input heat exchanger in a heatexchange relationship with the operating fluid in said heat sink meansto that heat from said first heat storage fluid is transferred to theoperating fluid in said heat sink means through said first output heatexchanger as long as the temperature of said first heat storage fluid isabove the working fluid vaporization temperature and higher than thetemperature of the operating fluid of said heat sink means passingthrough said first output heat exchanger to cause the vaporized workingfluid in said first output heat exchanger to condense and the condensedworking fluid to flow back into said first input heat exchanger underthe force of gravity for revaporization in said first input heatexchanger while heat is prevented from being transferred from theoperating fluid to said first heat storage fluid when fluid passingthrough said first heat exchanger is greater than the temperature ofsaid first heat storage fluid, and said second input heat exchangeroperatively connected to said second output heat exchanger for placingthe vaporized working fluid from said input heat exchanger in a heatexchange relationship with the operating fluid in said heat sink meansso that heat from said second heat storage fluid is transferred to theoperating fluid in said heat sink means through said second output heatexchanger as long as the temperature of said second heat storage fluidis above the vaporization temperature and higher than the temperature ofthe operating fluid of said heat sink means passing through said secondoutput heat exchanger to cause the vaporized working fluid in saidsecond output heat exchanger to condense and to flow back to said secondinput heat exchanger under the force of gravity for revaporization insaid second input heat exchanger while heat is prevented from beingtransferred from the operating fluid to said second heat storage fluidwhen the temperature of the operating fluid is greater than thetemperature of said second heat storage fluid.
 2. The heat transfersystem of claim 1 wherein the temperature of said first heat storagefluid is normally higher than the temperature of said second heatstorage fluid and wherein the operating fluid of said heat sink meanspasses first through said second output heat exchanger to initially heatthe operating fluid and then through said first output heat exchanger tofurther heat the operating fluid as long as the temperature of saidfirst heat storage fluid is higher than the temperature of said secondheat storage fluid.
 3. The heat transfer system of claim 1 wherein thetemperature of said first heat storage fluid is normally higher than thetemperature of said second heat storage fluid and wherein the operatingfluid of said heat sink means passes first through said first outputheat exchanger and then through said second output heat exchanger sothat heat is not transferred to the operating fluid from said secondoutput heat exchanger as long as the temperature of the operating fluidafter passage through said first output heat exchanger is higher thanthe temperature of said second heat storage fluid.